This invention relates to check valves, and more particularly to check valves employing dual seats and dual poppets wherein one set relies on a metal-to-metal or hard seal and the other set relies on a resilient or soft seal.
Many prior attempts have been made to develop a zero leakage, soft seat check valve, all without success. In each of these known efforts, the seal was required to seat and unseat under high pressures and flows. In many cases the seal is washed out from its containment groove during opening of the valve and experiences substantial errosion of the resilient seal during the closing cycle. The most effective zero leakage check valve available to date has been one commercially available from Bertea Products, known as a Micro-Seal check valve. This valve utilized two flat-lapped elements, one of which is provided with a pair of closely spaced, concentric, circular, sharp edged raised seats. The engaging surfaces must be maintained very flat and, as a result, the valve is very expensive to manufacture. This valve works reasonably well under most conditions. However, the valve will leak when the conditions are such that the valve seat closes slowly.